All About Space

Can dark matter emit dark light?

- Dr Keisuke Harigaya is a member of the School of Natural Sciences at the Institute for Advanced Study (IAS) at Princeton, New Jersey

We know little about the properties of dark matter. Various theories of dark matter, with or without dark light emission, have been proposed in the last few decades. Whether or not dark matter emits dark light is a key property that may allow us to pin down the theory of dark matter.

Theories of dark matter which emits dark light are constraine­d. In those theories dark matter interacts with itself by exchanging dark light. If the interactio­n occurs too frequently, the distributi­on of dark matter in galaxies becomes very different from what is inferred from the current observatio­ns of the gravitatio­nal potential made by dark matter. Recent studies show that if dark matter interacts with dark light with the same strength as protons do with ordinary light, dark matter must be more than a hundred times heavier than protons. The bound on the mass is weaker for weaker interactio­ns. As long as this constraint is satisfied, dark matter can emit dark light. Dark light should be almost invisible to us – otherwise dark matter is no longer dark.

 ??  ?? Right: If dark matter emitted light, it would no longer be dark
Right: If dark matter emitted light, it would no longer be dark
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